To sign out of your account, switch accounts, or manage your account settings, select your picture on the upper right side of the screen. If you see your email address at the top instead of a photo, select that.

The only apps you'll see in your list are ones you've received notifications from already. For example, you might get YouTube notifications over email, but, if you never received a YouTube notification in the Google bar, YouTube won't show up in this list.

Disabling notifications in the Google bar does not disable the notifications you receive from the same Google app on your phone, tablet or email. To turn off those notifications, check the settings in each app.